There is typically known an “auto throttle function” for a general-purpose engine used as a drive source such as power generator which uses a unit such as sensor to detect a load on the engine and reduces an engine frequency to a target rotational frequency (low idle) during no load, thereby decreasing noises and improving fuel efficiency.
There is also known a technique called “electronic governor” which controls a throttle aperture in CPU for an adjustment mechanism called governor mechanism which keeps a frequency of an engine constant. When achieving the auto throttle function by the technique, there is known a method for detecting a throttle aperture to estimate a load on an engine, and lowering a set frequency when the load is small.
In other words, when the auto throttle function is achieved by the electronic governor, the engine is started to end air warming, and then a target rotational frequency of the electronic governor is set at a low engine frequency (NEL) called low idle during no load. When the throttle aperture exceeds a preset threshold of the throttle aperture with increase in external load, the engine load is decided as “present” and the target rotational frequency is increased to a high engine frequency (NEH).
To the contrary, when the throttle aperture falls below the preset threshold of the throttle aperture with no load, the engine load is decided as “absent” and the target rotational frequency is lowered to the low engine frequency (NEL) as low idle.